[1] Unless I missed it, I did see the term VE [ volumetric efficiency ] mentioned. It becomes most important when selecting WOT carb airflow, no matter which 'formula' you use. A production engine at peak HP rpm might only have 75% VE. So if the formula calculates 600 cfm, the theoretical ideal carb cfm would be 450 cfm. At the other end of the scale, a full blown race engine might have a VE of 105% at peak HP rpm, so 630 cfm would be the ideal rating.
[2] Theoretical. So many other things to consider when selecting a carb, other than cfm. Booster types, pri/sec bore sizes etc. Plenty of examples of smaller cfm carbs making more HP than large cfm carbs because of better atomisation & distribution. Not all about size.
[3] TQs & QJs. A 750 QJ was used on the Aussie 253 Holden V8; it was also used on the 1967 Pontiac OHC in line six, which was 230 ci. This is the versatility of the air valve type carb. Many people think that these carbs on a smaller engine do not fully open the AV or the sec t/blades. They do. It is the pressure drop at WOT that changes with engine size.